3[1]ORE International Inc．7500 Series Flowmeter Technical Reference Manual 1994．
4[2]Atmel Corporation Nonvolatile Memory Data Book 1996．
5[3]E．Vargas R．Ceres J．M．Martin L．Calderon Ultrasonic sensor for liquid－level inspection in bottles Sensors and Actuators A61 1997 PP256259．
6[4]S．ROS J．M． Martin Abreu T． Freire and L．Calderon Digital techniques improve range measurement with ultrasound sensor Sensors and Actuators A32 1992 PP550554．
7[5]N．K．Abdulaziz S．D．Marougi Effect of an AGC amplifier on the performance of a generalized PLL in the presence of a large interfering signal IEE PROCEEDINGS Vol．136 Pt．G NO．4 AUGUST 1989 PP178183．
